Studies of two types of cataracts are being undertaken. In sugar cataracts, galactosemic and diabetic, it has been established that the enzyme aldose reductase triggers the cataractous process. Treatment with animals which are galactosemic or diabetic with an aldose reductase inhibitor effectively delays the onset of the cataracts. The second form of cataract is a hereditary type observed in the Nakano mouse strain. This is an osmotic cataract caused by a defect in the cation pump mechanism. The apparent deficiency in the Na-K ATPase appears to be due to an endogenous inhibitor of the enzyme.